Separation of thiophenols and tar acids



Oct. 27, 1959 D. c. JONES EI'AL 2,910,507

SEPARATION OF THIOPHENOLS AND TAR ACIDS Filed Feb. 6. 1958 MAKEUP METHANOL v o 5::3 4d

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' XTRlCTANT IN V EN TORS DONALD C. JONES MARTIN BFNEUWORTH United States Patent SEPARATION OF THIOPHENOLS AND TAR ACIDS Donald C. Jones and Martin B. Neuworth, Pittsburgh,

Pa., assignors to Consolidation Coal Company, Pittsburgh, Pa., a corporation of Pennsylvania Application February 6, 1958, Serial No. 713,624

16 Claims. (Cl. 260-609) This invention relates to the art of refining tar acids, and more particularly, to the use of a cycloparaflin solvent in a double-solvent extraction process for removing thiophenols from a mixture containing tar acids and thiophenols. The process described herein is an improvement over that described in US. Patent 2,767,220, issued to Martin B. Neuworth, one of the co-inventors of this invention.

In US. Patent 2,767,220, a method is shown for removing thiophenols from a thiophenol-containing tar acid feedstock that is substantially free of neutral oils. These feedstocks may contain from 0.5 to 25 percent by weight of thiophenols, such as thiophenol itself, thiocresols, thioxylenols, etc. Disulfides, formed by the oxidation of thiophenols, are also generally present. In the patented process, the feedstock is contacted with aqueous methanol and with a low-boiling paraflinic naphtha fraction in a continuous countercurrent extraction zone. The mixture of thiophenols and tar acids is fed to a point intermediate the ends of the extraction zone. Where a vertical extraction zone is used, the aqueous methanol solution is fed at the top of the vertical extraction zone, and passes down through the zone dissolving substantially all the tar acids. The naphtha fraction is fed upwardly through the vertical extraction zone in countercurrent relation to the aqueous methanol solution, and passes through the extraction zone dissolving the thiophenols and any residual neutral oil that may be present.

The relative proportions of the three liquids present, namely, the feedstock, the aqueous methanol, and the naphtha fraction, determine the yield or recovery of tar acids, the purity of the tar acids with respect to thiophenol and disulfide content, and the feed rate or throughput of the feedstock through the extraction zone.

For a given solvent system, temperature, and column design, the ratio of naphtha fraction to feedstock generally serves to control the purity of the tar acids with respect to thiophenol and disulfide content; the ratio of aqueous methanol to paratfinic naphtha fraction generally controls the recovery of the tar acids; and the ratio of the feedstock to the combined naphtha fraction plus aqueous methanol serves ordinarily to determine the throughput of the feedstock through the column, namely, the rate at which the feedstock can be fed through the extraction column. For a given set of parameters, the present invention results in increased tar acid throughput, purity and/ or yield compared with the prior art process.

It is accordingly an object of the present invention to produce tar acids of improved purity with respect to thiophenol content while using a predetermined ratio of thiophenol-extracting solvent to feedstock.

It is a further object to provide tar acids of improved purity with respect to thiophenol content for a given set of tar acid recovery and throughput conditions.

It is yet a further object to provide a tar acid recovery system having improved throughput for a preselected set of conditions of tar acid recovery and tar acid purity with respect to thiophenol content.

2,910,507 Patented Oct. 27, 1959 As a feature of the present invention, for a given ratio of thiophenol-extracting solvent to feedstock, tar acids of improved purity with respect to thiophenol content are obtained by using a cycloparaffin solvent as the major or principal component of the thiophenol extractant. More specifically, the cycloparafiin solvent used has from six to eight carbon atoms and is selected from the group consisting of alkyl-substituted cyclopentanes, cyclohexane, alkylsubstituted cyclohexanes, and mixtures thereof. This improvement in tar acid purity is obtained without necessarily considering the effect upon feedstock throughput.

Additionally, by use of a particular thiophenol-extracting solvent blend of cycloparaifin and of naphtha fraction, an improvement in the purity of the tar acids with respect to thiophenol content may be obtained while maintaining the feedstock throughput substantially the same as in the prior art process; or, conversely, for a predetermined level of tar acid purity with respect to thiophenol content, the throughput of the feedstock through the column is markedly increased. The foregoing may be accomplished by using a thiophenol-extracting solvent blend having a density below 0.80 comprising at least 40 percent of cycloparaffin, the balance consisting of a parafiinic naphtha fraction boiling below 130 C. The naphtha fraction is substantially the same as that used in the process described in US. Patent 2,767,220.

Somewhat surprisingly, it has been found that the use of a thiophenol-extracting solvent consisting of either cycloparaflin alone or a cycloparaflin-naphtha blend is effective in a double-solvent extraction process for re fining tar acids only Where the tar acids are substantially free of neutral oil. For example, US. Patent 2,666,796 discloses the refining of a tar acid oil by a double-solvent extraction process employing aqueous methanol and naphtha. However, if the naphtha in that process is replaced by either a cycloparafiin alone or a cycloparaffinnaptha blend, poor separation results. The process of this. invention, therefore, is considered uniquely directed to the refining of tar acids substantially free of neutral oil.

For a more detailed description of this invention, in accordance with the objects and features thereof, reference should be made to the sole figure of the drawing, which is a diagrammatic illustration of apparatus adapted for the practice of this invention.

Referring to the drawing, a thiophenol-containing tar acid feedstock is pumped continuously from a storage tank 10 through a pipeline 12 into a continuous countercurrent double-solvent extraction zone consisting in the preferred embodiment illustrated of a vertical center feed extraction column 14. The feedstock is substantially the same as that described in US. Patent 2,767,220, and is conventionally obtained by the extraction of petroleum distillates with an aqueous caustic solution. The feedstock generally, but not necessarily, has a boiling range from about 160 C. to about 300 C., or some part thereof, particularly the fraction boiling up to 230 C. The extraction column is substantially of the same design as that described in the afore-mentioned patent.

The aqueous methanol solution is fed continuously from an aqueous methanol storage tank 16 through a pipeline 18 into the top of extraction column 14. It is necessary to employ an aqueous methanol solution containing from about 40 to 90 percent by weight of methanol, and preferably from 55 to percent by weight of methanol. In concentrations below about 40 percent methanol, recovery of tar acids becomes too low to be practical. Above about percent methanol concentration, the methanol solution dissolves the thiophenols so that the extracted tar acids remain contaminated to an undesir able extent.

The thiophenol-extracting solvent, consisting of the cycloparafiin of this invention used either alone or in admixture with the paraffinic naphtha fraction, is fed continuously from a thiophenol extractant storage tank through a pipeline 22 into the base of extraction column The cycloparaffins found suitable in the practice of this invention have from six to eight carbon atoms, and are selected from the group consisting of valkyl-substituted cyclopentanes, cyclohexane, alkyl-substituted cyc'lohexanes, and mixtures thereof. Surprisingly, cyclopentane has been found to be unsuitable for the practice of this invention insofar as yielding improved results for a given set of extraction parameters. Particularly preferred in the practice of thisinvention are the cycloparaflins methylcyclopentane, cyclohexane, and methylcyclohexane.

The cycloparalfins of this invention, for a given ratio of thiophenol-extracting solvent to feedstock, give improved results compared with'the' use of the-naphtha fraction alone for thiophenol extraction. Thus, where the purity of the tar acids is of prime importance, and the throughput of the feedstock through the column is a relatively minor consideration, the use of the cycloparaflins as sole thiophenol-extracting solvent is preferred. It has been found, however, using the cycloparaflin alone, that in order to obtain this improved purit, the same throughput as practiced in the prior art process cannot be maintained. Thus if an attempt is made to use the cycl'oparaffin alone at the same feedstock throughputas used for the naphtha fraction alone, flooding of the extractioncolumn occurs. However, when a-mixed thiophenol-extracting solvent blend is used comprising at least 40 percent by weight of the cycloparaflin, the balance comprising the parafiinic naphtha fraction, the feedstock throughput is affected only slightly Whereas the purity of the tar acids is markedly improved. Therefore, Where maintenance of the throughput of the feedstock is of primary importance, a thiophenol-extracting solvent blend should be used. The preferred thiophenol-extracting solvent blend comprises from about 40 to 60 percent by weight of cycloparaflin and from about 60 to 40 percent by weight of parai'finic naphtha fraction. The naphtha fraction must be essentially parafi'lnic in character. Such solvents may be obtained from the distillation of paraffinic petroleum stocks. The boiling range of the naphtha fraction should be 60 to 130 C., and the density of the naphtha fraction should preferably be less than-0.80. The hexane cut of paraffinic naphtha is preferred as the naphtha'fraction used in the cycloparaffin-naphtha blend. Inasmuch as certain naphtha fractions, such as commercial hexane,.may contain slight amounts of-cycloparaffins as contaminants, but always well below the required amount, such naphtha fractions may be enriched with additional amounts of thedesired cycloparaffin to obtain the required ratio of cycloparafiin to naphtha fraction in the blend. All ratios reported herein of cycloparafiin to naphtha fraction are on an assumed basis of a cycloparafiin-free naphtha fraction.

Where a tar acid product of no higher purity than is obtained with a parafiinic naphtha fraction alone is desired, then the throughput of the feedstock may be materially increased by using a cycloparaflin-naphthablend. Or, if the purity of the tar acids and the feedstock throughput are kept unchanged, the required ratio oftotal solvent to feedstock is substantially reduced. This effectively results in a saving of almost 50 percent 'inthe amount of total solvent, i.e., thiophenol extractant and aqueous methanol, required for extraction of the thiophenols. In addition, considerable fuel savings result from the fact that smaller amounts of solvents have to be recovered in the subsequent solvent distillations.

Ordinarily, the same relative volumes of feedstock to aqueous methanol to thiophenol extractant may be used asemployed in the patented process. Thus, for every volume of feedstock used, from 0.5 to 5.0 volumes .of aqueous methanol and from 0.5 to 5.0 volumes of thiowhether the thiophenol extractant consists of the cycloparaffin alone or of the cycloparaflin-naphtha blend. The ratio of aqueous methanol to thiophenol extractant should be controlled according to the solvent that is selected as the continuous phase. When the thiophenol-extracting solvent is employed as the continuous phase, it is necessary for maintaining desired yields and purity to regulate the solvent ratio so that the volume of aqueous methanol is from 0.25 to 4.0 times the volume of thiophenol extractant. When aqueous methanol .is employed asthe continuous phase, the solvent ratio should be regulated so that the volume of aqueous methanol is from 0.5 to 2.0 times the'volume of thiophenol extractant. It is generally preferred to employ the thiophenolrextracting solvent as the continuous phase.

Substantially the same apparatus and techniques are also employed in the practice of this invention as in the practice of the invention described in U.S. Patent 2767,- 220. 'For example, the aqueous methanol extract containing tar acids is withdrawn continuously fromthe bot tom of extraction column 14 through a pipeline 24 and fed into a distillation column 26. The purified tar acids and the water leave distillation column 26 as bottoms through a pipeline 28 and pass into a phase separation tank 30. A cooler 32 may be used to cool the waterand tar acids passing throughpipeline 28. The purified tar acids are withdrawn as product through a pipeline 34. The aqueous phase from the phase separation tank'30 is withdrawn through a pipeline 36 and sent to the aqueous methanol storage tank '16 for recirculation.

Anhydrous methanol passes overhead'from distillation column 26 through a pipeline 38 to a reflux condenser 40. It then passes through a pipeline 42 to the aqueous methanol storage tank 16 for recirculation. Aportion of the condensed methanol is returned through a pipeline 44 to the top of distillation column 26 as reflux. Fresh methanol may be added to the aqueous methanol storage tank 16 from a pipeline 46 to make up the desired'concentration.

The thiophenol extractant with the dissolved thiophenols and any residual neutral oil and aryl disulfides leaves the top of extraction column 14 through a pipeline 48 and passes to a distillation column 50 where the thiophenol-extracting solvent is separated from the thiophenols. The thiophenol-extracting solvent passes overhead from distillation column 50 through a pipeline 52 and a reflux condenser 54. A portion of the condensed thiophenol extractant may be circulated through a pipeline 56 as reflux for distillation column 50. The remainder of the thiophenol extractant is returned to the thiophenol extractant storage tank 20 through a pipeline 58 for recirculation. Thiophenols leave distillation column 50 as the bottom-product'through a pipeline-60. A cooler 62 may be inserted in pipeline 60 to cool the thiophenols.

A comparison between a typical naphtha fraction, such as commercial grade hexane, and some typical cycloparaffins with respect to eificiency in removing thiophenol from a mixture of 12 to 15 percent by weight thiophenols and the balance tar acids was made. Th composition and properties of the thiophenol-extracting solvents used are shown in Table I.

In Table II'is shown a comparison between the hexane and the cycloparaffin samples ,as thiophenol extractants for a given set of extraction conditions.

A total throughput of feedstock and solvents of 37 .5 milliliters per minute was used for all runs shown in Table'll. The aqueous methanol consisted of 60 per-- cent by weight of methanol in water. The commercial hexane contained, as commercially occurring contaminants, about 15 percent by weight of a mixture of methylcyclopentane and cyclohexane.

As shown in Tablell, all of thecycloparafiins tested, with the exception of cyclopentane, proved superior to commercial hexane in remo ing on m na ing thioyielded tar acids having a content of 0.01 percent or less of sulfur compounds, as thiocresols. Thus for comparable feedstock throughput and solvent feed rates, the cyclohexane-hexane blend have a more than fivefold improvement compared with hexane alone.

EXAMPLE 2.-VERY HIGH PURITY TAR ACIDS Where the obtaining of very high purity tar acids with respect to sulfur content is of primary importance, but feedstock throughput is still a consideraiton, a thiophenolextracting solvent blend consisting of 60 parts of commercial heptane, calculated on a cycloparaffin-free basis, and 40 parts of commercial methylcyclohexane is con- The commercial heptane may contain about 25 percent methylcyclohexane. It has a specific gravity of 0.724i0005 at 60/60 F. and a maximum distillation range of 2032ll F., ASTM The commercial grade methylcyclohexane contains at least 75 percent methylcyclohexane, has a specific gravity of 0.770: ;0.0l at 60/60 F. and has a maximum distillation range of 205215 F. Because of the slightly higher specific gravity of the methylcyclohexane-heptane blend compared with the blend of Example l, the feedstock may have a slightly lower maximum throughput through the extraction column that occurs TABLE I T hiophenol-extracting solvents Thiophenol extractant Grade Properties istillation range: 150160 F. Hexme Phillips commmlal S pecific gravity, 60l60 F., 0,690. 1 d {Distillation range: 124-135 F. Wentan Specific gravity, s eo 11, 0995. Methylcyclopentane-.. Phillips, technical (min. 95 molepercent) I o ye o e a e Phillips. c e cia 5- I O Methyleyc1ohexane Phillips, technical (min. 95 mole percent) [560 F TABLE 11 Hexane vs. cycloparaflins as thiophenol extractants sidered particularly suitable. Feed rate, volume per Th1ounit time Relative phenol feedstock (and throughdisultide) Thiophenol extractant Aque- Thioput, content of Feedous phenol feedstock extracted D 216-53 stock methextraetrate/total feedstock,

anol ant rate weight percent Hexane 1 1. 5 3 0.182 0. 05 Cyclopentane l 1. 5 3 0. 182 0. 047 Methylcyclopentane l 1 5 3 O. 182 0.009 Cyclohexane l 1 5 3 0.182 0.005 Methylcyclohexane..." 1 1 5 3 0.182 0.001 Hexane (modified solvent ratio) 1 2 4.5 0.133 0.006

EXAMPLE 1.IMPROVED PURITY----SAME THROUGHPUT Particularly preferred in the practice of this invention to obtain a tar acid product having a low concentration of thiophenols, while maintaining the feedstock throughput through the extraction column substantially unchanged as compared with that shown in the process of US. Patent 2,767,220, is a thiophenol-extracting solvent blend consisting of parts by weight of a commercial hexane, calculated on a cycloparafiin-free basis, and 50 parts by weight of a commercial cyclohexane. The hexane used in the blend was a commercially available hexane containing about 15 percent by weight of a mixture of methylcyclopentane and cyclohexane. This hexane solvent has a specific gravity of 0690:0005 at /60 F. and a distillation range of 150460 F., ASTM Test D-2l653. The cyclohexane was a commercial cyclohexane obtained from the Phillips Petro leum Company and containing approximately -85 percent cyclohexane; it had a specific gravity of 0.775 r0005 at 60/ 60 F. and a maximum distillation range of F. The impurities most probably present in the commercial grade cyclohexane were 2,2,3-trimethylbutane, 2,4-dimethylpentane, and 2,2-dimethylpentane.

Two runs were made under comparable conditions in which a feedstock containing approximately 15 percent by weight of thiophenols was used. The total throughput of feedstock and solvents for both runs and 99 milliliters per minute, and the solvent ratio used in both runs was 1/ 1.5/3 (feedstock/ 60 percent by weight aqueous methanol/extractant). Using the commercial hexane extractant, tar acids having a sulfur content, as thiocresols, of 0.05 percent were obtained. The comparable run made with the above cyclohexane-hexane blend in Example 1. However, using the niethylcyclohexaneheptane blend, tar acids may be obtained having less than 0.004 percent thiophenols. This is of higher purity than is obtainable with the blend of Example 1.

EXAMPLE 3.COMPARISON OF THIOPHENOL EXTRACTANTS Thirteen different thiophenol-extracting solvents were compared for their efiiciency in removing sulfur impurities and for their eifect on feedstock throughput. Included in this comparison were three hexane samples, heptane, cyclohexane, cyclopentane, methylcyclohexane, and various combinations of a hexane with a particular cycloparafiin of the group mentioned. Each of the sol vents was a commercial grade solvent except for methylcyclopentane and methylcyclohexane, which were both of technical grade. A petroleum-derived feedstock substantially free of neutral oil was used, with 60 percent aqueous methanol being used as solvent therefor. In all instances, a 28-stage, one-inch inside diameter glass extraction column was used; the ambient temperature was 2325 C., except where otherwise noted.

It was found that while no particular effect on recovery of tar acids could be attributed to the thiophenolextracting solvent composition used, some rather striking difierences in product purity were observed. The cycloparafiin-paraflin blends were found to be more effective as thiophenol extractants than the parafiins alone, giving tar acids of equivalent or higher purity at lower solvent ratios. For example, using solvent blends consisting of methylcyclopentane, methylcyclohexane, and mixtures of these with hexane, as well as the cycloparaflins alone, resulted in tar acids containing from 0.001 to 0.01. percent sulfur compounds at solvent ratios of 1/ 1.5/3 (feedstock/60 percent aqueous methanol/thiophenol extractant). Hexane alone at this solvent ratio gavetar acids containing 0.079 percent sulfur compounds; solvent ratios of 1/2/45 using hexane alone were required to give tar acids containing 0.012 percent sulfur compounds. Thus a total solventto feedstock ratio of 6:1 was needed with hexane alone in order to obtain the same degree of purification as was obtained when using a 45:1 ratio with the thiophenol-extracting solvent blend.

It was also found that cycloparaffins tend to flood at lower throughputs than do commercial hexanes. For example, in a run at C., cyclohexane flooded at total throughputs above 37.5 milliliters per minute, l/.1.5/ 3 (feedstock/aqueous methanol/thiophenol extractant), or 6.8 milliliters per minute feedstock throughput. exane, on the other hand, flooded at total throughputs greater than 135-150 milliliters per minute, 1/2/45, or 18-20 milliliters per minute feedstock throughput. However, a mixture of 65 percent cyclohexane and percent hexane was operable at 99 milliliters per minute, 1/ 1.5 /3, or 18 milliliters per minute feedstock throughput. This mixture gave tar acids having a purity comparable to that obtained with hexane at the same feedstock throughput, namely 18 milliliters per minute; however, the thiophenol-extracting solvent blend required a total solvent to feedstock ratio of but 4.5:1 (1/l.5/3) compared to 6.511 (1/2/45) when using a hexane solvent. This lower ratio for the blend results in a substantial saving in the amount of total solvent, i.e., aqueous methanol and thiophenol extractant, initially required as well as savings in the subsequent distillation step used for recovering the methanol and the thiophenol extractant. These results are summarized in Table 111.

.It was found that temperature was an important consideration in the case of extractions made using a cycloparaffin alone. Thus in an extraction made with cyclohexane alone as thiophenol extractant, solvent ratios that resulted in flooding at 23 C. were satisfactory when the system was operated at 30 C. In general, the higher the cycloparafin content of the thiophenol extractant, the higher the temperature required, within the range of 15-4 5 C.

For optimum over-all conditions of operation, it may therefore be concluded that the preferred thiophenolextracting solvent should contain a considerable percentage of cycloparafiins, preferably at least percent by weight of the thiophenol-extracting blend. Commercially available hexanes themselves may contain as much as 15 to 20 percent methylcyclopentane, but always well below the preferred cycloparaffin content of at least 40 percent by weight. Hence to achieve a total concentra- TABLE III Cycloparafiins, naphtha and cycloparafiin-naphtha blends tion of, for example, 65 percent methylcyclopcntane by weight, it is necessary to enrich a naphtha fraction that may already contain, for example, 20 percent by weight of methylcyclopentane by adding thereto the appropriate amount of commercial methylcyclopentane. In general, thiophenol-extractant efficiency of the preferred cycloparaffins has been found to be, in descending order: methylcyclohexane, cyclohexane, methylcyclopentane.

Where either a cycloparafiin alone or a cycloparaifinnaphtha fraction blend is used as thiophenol-extracting ..heptane with. methylcyclohexane.

solvent, the density thereof should be less than 0.80and preferably less than 0.75. This ensures a gravity difference between the .two phases in the extraction column sufiicient to effect a ready separation of the phases. Inasmuch as the cycloparafiins preferred for use generally have a greater density than the naphtha fraction employed, the latter should also preferably be less than 0.80 to ensure an over-all density .of the blend of less than 0.80. The hexane and heptane cuts of paraflinic naphtha are preferred in this regard.

it is considered preferable, because of specific gravity considerations in preparing mixed cycloparaflin-naphtha fraction blends, to fortifyhexane with cyclohexane, and

, Th p o es for pa i g th op e l fr a mix ture containing thiophenols and tar acids that is substantially free of neutral oil which comprises the steps of feeding said mixture to an extraction zone, feeding an aqueous methanol solution containing about 40 to weight percent methanol and the balance water to one end of said extraction zone, feeding a thiophenol-extracting solvent comprising as principal component a cycloparafiin having from six to eight carbon atoms and selected from the group consisting of alkyl-substituted cyclopentanes, cyclohexane, alkyl-substituted cyclohexanes and mixtures thereof to the other end of said extraction.

zene, passing said aqueous methanol solution and said thiophenol-extracting solvent through said extraction zone in countercurrent relation, and recovering the aqueous methanol extract containing tar acids.

2. The process of claim 1 wherein said thiophenolextracting solvent is a cycloparafiin-enriched naphtha fraction.

3. The process of claim 1 wherein the cycloparafiin is methylcyclopentane.

4. The process of claim 1 wherein the cycloparaifin is cyclohexane.

5. The process of claim 1 wherein the cycloparaflin is methylcyclohexane.

6. The process for separating thiophenols from a mixture containing thiophenols and tar acids that is substantially free of neutral oil which comprises the steps of feeding said mixture to an extraction zone, feeding an aqueous methanol solution containing about 40 to 90 weight percent methanol and the balance water to one end of said extraction zone, feeding to the other end of said extraction zone a thiophenol-extracting solvent having a density of less than 0.8 comprising a mixture of (a) at least 40 percent by weight of a cycloparafiin having from six to eight carbon atoms and selected from the group consisting of alkyl-substituted cyclopentanes, cyclohexane, alkyl-substituted cyclohexanes and mixtures thereof, and (b) the balance consisting of a paraffinic naphtha fraction boiling within the range of 60m C., passing said aqueous methanol solution and said thiophenol-extracting solvent through said extraction zonein countercurrent relation, and recovering the aqueous methanol extract containing tar acids.

7. The process of claim 6 wherein the paratfinic naphtha fraction is a hexane cut of petroleum naphtha.

8. The process of claim 6 wherein the cycloparaffin is methylcyclopentane.

9. The process of claim 6 wherein the ,cycloparaffin is cyclohexane.

10. The process of claim 6 wherein the cycloparaffin met yl y lohexane However, it .will of.

1-1. The process of separating thiophenols from tar acids which comprises the steps of feeding a mixture consisting essentially of tar acids and thiophenols, said mixture boiling above 160 C. and below 300 C., to a vertical extraction zone at a point intermediate the ends thereof, feeding an aqueous methanol solution containing 55 to 75 weight percent methanol and the balance water to the top of said vertical extraction zone, feeding to the bottom of said vertical extraction zone a thiophenol-extracting solvent having a density of less than 0.8 comprising (a) at least 40 percent by weight of a cycloparaflin having from six to eight carbon atoms and selected from the group consisting of alkyl-substituted cyclopentanes, cyclohexane, alkyl-substituted cyclohexanes, and mixtures thereof and (b) the balance of a paraflinic naphtha fraction boiling within the range of 60 to 130 C., circulating said aqueous methanol solution downwardly and said thiophenol-extracting solvent upwardly through said vertical extraction zone in countercurrent relation, regulating the rate of Withdrawal of said methanol solution and said thiophenol-extracting solvent from said extraction zone so that the thiophe'nol-extracting solvent phase is the continuous phase, regulating the feed rate so that at least 0.5 and not more than 5.0 volumes of said aqueous methanol solution and at least 0.5 and not more than 5.0 volumes of thiophenol-extraeting solvent are fed to said extraction Zone for every volume of said mixture of tar acids and thiophenol fed to said extraction zone, and separately recovering the aqueous methanol extract containing tar acids and the thiophenol-extracting solvent extract containing thicphenols.

12. The process of claim 11 wherein the cycloparaflin is methylcyclopentane.

13. The process of claim '11 wherein the cycloparaflin is cyclohexane.

14. The process of claim 11 wherein the cycloparaflin is methylcyclohexane.

15. The process of claim 11 wherein the paraflinic naphtha fraction is a hexane cut of petroleum naphtha.

16. The process of claim 11 wherein the paralfinic naphtha fraction is heptane and the cycloparaffin is methylcyclohexane.

References Cited in the file of this patent UNITED STATES PATENTS UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No, 2,910,507 October 2'7, 1959 Donald C'. Jones et al0 It is hereby certified that error appears in the-printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

.Column 5 line 39, Table II, sixth column thereof, fifth line, for "0.001" read Less than 0.001 line 69 for "and", second occurrence, read Was column 6, line 4, for "have" read gave w Signed and sealed this 19th day of April 1960.,

(SEAL) Attest:

KARL H, AXLINE ROBERT C. WATSON Attesting Officer Commissioner of Patents 

1. THE PROCESS FOR SEPARATING THIOPHENOLS FROM A MIXTURE CONTAINING THIOPHENOLS AND TAR ACIDS THAT IS SUBSTANTIALLY FREE FO NEUTRAL OIL WHICH COMPRISES THE STEPS OF FEEDIND SAID MIXTURE TO AN EXTRACTION ZNE, FEEDING AN AQUEOUS METHANOL SOLUTION CONTAINING ABOUT 40 TO 90 WEIGHT PERCENT METHANOL AND THE BALANCE WATER TO ONE END OF SAID EXTRACTION ZONE, FEEDING A THIOPHENOL-EXTRACTING SOLVENT COMPRISING AS PRINCIPAL COMPONENT A CYCLOPARAFFIN HAVING FROM SIX TO EIGHT CARBON ATOMS AND SELECTED FROM THE GROUP CONSISTING OF ALKYL-SUBSTITUTED CYCLOPENTANES, CYCLOHEXANE, ALKYL-SUBSTITUTED CYCLOHEXANES AND MIXTURES THEREOF TO THE OTHER END OF SAID EXTRACTION ZONE, PASSING SAID AQUEOUS METHANOL SOLUTION AND SAID THIOPHENOL-EXTRACTING SOLVENT THROUGH SAID EXTRACTION ZONE IN COUNTERCURRENT RELATION, AND RECOVERING THE AQUEOUS METHANOL EXTRACT CONTAINING TAR ACIDS. 